The present invention is directed to a spraying system for spraying one or more materials onto a mold used for producing molded components. More specifically, the present invention comprises a system that can spray one or more materials onto a mold, such as a die-cast mold, while the mold is located in a molding machine running with a short cycle time, and wherein the supply pressure of the materials can be sufficiently maintained despite the high frequency of machine cycles.
While the spraying system of the present invention may be applicable to a variety of molding processes, for purposes of simplicity and clarity, the spraying system will be described below only with respect to its use in a die-casting process. Die-casting is a well known process whereby metallic components can be quickly and accurately molded from a molten metal. Metals commonly employed in die-casting operations may include, for example, aluminum, zinc, brass and magnesium. Modern die-casting processes are able to create products with good dimensional tolerances and appearance. Die-casting is often used to produce components for, among others, the automotive, industrial, electronics, and building product industries.
The die-casting process is similar to that of injection molding, with a significant exception being the substitution of a molten metal material for a molten plastic material. Once the design of a desired component has been generated, a die-cast mold is manufactured to produce the component. Die-cast molds are commonly produced from tool steel or one of a multiplicity of metal-alloys. Like plastic injection molds, die-cast molds generally have two halves, consisting of a cavity side and a core side. There may also be moveable cores on such a mold that can be moved into position during molding and then later retracted to facilitate removal of the molded component from the mold.
Once a satisfactory die-cast mold is produced, the mold is placed in a die-casting machine. Die-casting machines are typically horizontally oriented injection-type machines having a fixed platen and a moving platen for holding the separate halves of the die-cast mold. The moving platen is typically moveable with respect to the fixed platen along a series of tie bars and guide plates, such that the mold halves may be brought into contact during the molding cycle of the machine and then withdrawn to allow for removal of the molded component. The moving platen is typically caused to move via hydraulic power, although electric power has also been used. An apparatus is provided at the die-casting machine for supplying molten metal for the molding process. With the mold halves in forced contact between the fixed and moving platens of the die-casting machine, a hydraulic plunger forces a predetermined amount of the molten metal to travel through an injection barrel and into the mold. The molten metal is then held within the mold, under pressure, while the molded component cools or cures. After a predetermined amount of time the moving platen and accompanying mold half are withdrawn, and the molded component is ejected from the mold half or is withdrawn by a secondary device, such as a part removal robot.
In order to effectuate removal of a molded part from a mold it is generally necessary to treat at least the portions of each mold half contacted by the molten metal material with a release agent. The release agent essentially forms a thin barrier between the surfaces of the mold and the molten metal, thereby helping to prevent the molten metal from bonding to the mold. Because injection of the molten metal into the mold and subsequent removal of the molded component therefrom substantially removes or degrades the release agent, it is typically necessary to apply release agent to the mold prior to each molding cycle.
During the molding process, molten metal material may creep into small defects in the mold, or may partially invade the parting line that occurs between the flush-mating surfaces of the mold halves. This may result in the formation of what is typically referred to as flashxe2x80x94thin areas of excess material that are often attached to a molded component. Portions of this flash can often become detached from the molded component during separation of the mold halves or during removal of the component from the mold. These detached portions can remain on various portions of either mold half, such as on a core or cavity portion, or on the flat, mating surfaces that form the shut-off between the mold halves. Flash, or other contaminants that find their way onto the mold can cause defects in one or more subsequently molded parts, or may, if allowed to build up, prevent complete mating of the mold halves. To prevent such a situation from occurring, the mold halves are preferably cleaned off in between each molding cycle. As it would not be practical to perform a hand-cleaning of die-cast molds between molding cycles, cleaning is typically accomplished using high-pressure air. The high-pressure air is directed against each mold half to dislodge any flash or other contaminants that may be residing thereon.
Due to the molten state of the metal used to form die-cast components, die-cast molds typically become extremely hot during the die-casting process. As a consequence, it is generally necessary to cool a die-cast mold while in use, so that the mold temperature can be maintained within a desired range and so that the components molded therein can properly cool in an acceptable period of time. To this end, die-casting operations usually employ a chilled water system to supply chilled water to the die-cast mold. The chilled water may be moved through passageways occurring within the mold halves. Additionally, in order to assist in the cooling of the mold, it is also desirable to spray, or otherwise apply a die-lubricant to the molding surfaces of the mold halves between machine cycles.
In order for die-casting to be cost-effective, it is typically necessary that a large quantity of die-cast components be produced. In this manner, it is possible to spread out the cost of what is often a costly die-cast mold over a large number of components molded therefrom. To facilitate cost-effectiveness, it is also desirable that the die-casting machine used to produce the components be operated in the most efficient manner. Thus, the fastest molding cycle possible is usually sought out. To obtain a fast molding cycle, it is essential that part removal and any mold preparation, such as that previously discussed, be performed as quickly as possible. The requirement of haste, as well as safety, dictates that hand-cleaning of the mold halves and hand-application of a release agent and/or other substances thereto is not possible. As such, each of these processes is typically administered to by an automated device or devices.
Automated devices for performing die-cast mold cleaning and/or the application of release agents and other substances thereto, must perform their particular function within a limited amount of time. The faster the die-cast machine cycle, the less time available for these ancillary functions. Earlier, known devices placed spraying mechanisms on retractable cylinders, or masts, that could be lowered into the space between the mold halves once the molded component had been removed. However, these known devices had several undesirable characteristics, such as, for example, the residing thereof directly over the mold halvesxe2x80x94which could allow for such a device to fall between the mold halves during certain portions of the molding cycle. Consequently, other systems have been developed that do not require the spraying device to reside substantially over the meeting point of the mold halves, but still allow the spraying mechanism to be lowered into the open mold between machine cycles. While these known systems may recite methods of moving a spraying device into position between the mold halves, they have not considered other problems inherent with short cycle-time die-cast molding; namely, effecting proper cooling of the die-cast mold, and maintaining sufficient supply pressures so that release agents, air, and other substances may be quickly and acceptably applied to the mold. The present invention addresses these problems.
The present invention is directed to a system for providing the necessary mold spraying operationsxe2x80x94particularly with respect to a short cycle-time molding operation, such as die-cast molding. The present invention recites an automated spraying device that preferably employs a spray head mounted to a manipulator arm. The manipulator arm is preferably mounted on a top of surface of the die-casting machine or, alternatively, to the top of the fixed platen of the machine. The path and range of motion of the manipulator arm are preferably adjustable, thereby allowing the spray head to be lowered between open mold halves at the appropriate time during the molding cycle. The spray head also employs novel supply circuitry that allows a supply of pressurized air, release agent, and/or other materials to be applied to the mold halves at a sufficient and substantially constant pressure, even if there is a decrease in the supply pressure of the materials. In order to effectuate proper cooling of the die-cast mold, a die-lubricant is preferably one of the materials applied to the mold halves by the spray head, either independently, or as a mixture with another material. The design of the supply circuitry utilizes a pressure boosting unit that permits the spray head to apply the desired materials at a substantially constant pressure, even when used on die-casting machines having extremely short cycle-times. Preferably, operation of the spray system is governed by a control device, such as, for example, a series of relays and contacts, a personal controller or, more preferably, a programmable logic controller (PLC).